Vapor deposition coating apparatus



April 17, 1962 J. z. CERYCH ETAL 3,029,777

VAPOR DEPOSITION'COATINGAPPARATUS Filed Jan. 30, 1959 2 Sheets-Sheet 1TO \ACUUM PUMP COPPER FIGURE l.

April 17, 1962 J. z. CERYCH ETAL VAPOR DEPOSITION COATING APPARATUS 2Sheets-Sheet 2 N mmnmI uomnow had:

Filed Jan. 30, 1959 muamou ZPDOZ Mom ,I

a? Q A w m =oo 3000 Jill/[ll @fiiied rates Patent VAPOR DEPGSITIONCOATING APPARATUS John Z. Cerych, Methuen, Philip J. Clough, Reading,

and Robert W. Steeves, Nahant, Mass, assignors to National ResearchCorporation, Cambridge, Mass., a

corporation of Massachusetts Filed Jan. 31 1959, Ser. No. 790,274 3Claims. (Cl. 118-49) This invention relates to coating and moreparticularly to coating by vapor deposition of a metal or other materialunder high vacuum conditions. The invention particularly directed to thedesign of an improved source of vapors.

It is a principal object of the present invention to provide an improvedsource of coating vapors for coating a substrate in an evacuatedchamber.

Another object of the invention is to provide a source of metal vapors,which source has a long operative life.

Still another object of the invention is to provide sources of the abovetype which are relatively inexpen-' sive to manufacture and which aresimple to maintain.

Another object of the invention is to provide sources of the above typewhich are very efiicient and can be designed for numerous types of heattransfer.

Reference should be had to the following drawings wherein FIG. 1 is asectional, diagrammatic, schematic View of one preferred embodiment ofthe invent-ion, and FIG. 2 is a sectional, diagrammatic, schematic viewof a portion of FIG. 1 taken along the line 22.

In the present invention there is provided a vaporization chamber(preferably a coating chamber) in which the coating material isevaporated. The substrate to be coated is preferably passed through thecoating chamber and it is coated by condensation of the vapors on thesurface of the substrate. For convenience of illustration, the inventionwill be initially described in connection with the vapor deposition ofaluminum on a continuous substrate such as sheet steel without anyintent to limit the invention to this specific preferred embodiment.When so utilized, the coating chamber includes a support for holdingmolten aluminum, the support preferably comprising a carbonaceouscrucible having a surface of boron nitride, Zirconium carbide or othermaterial which is relatively inert to molten aluminum at elevatedtemperatures. There is also provided a molten bath which is maintainedin contact with the support for the molten aluminum, this molten bathbeing for the purpose of transferring heat to the support and the moltenaluminum to vaporize the aluminum. There is also a heater formaintaining the molten bath at a suiiiciently high temperature that themolten aluminum is heated to a temperature where its vapor pressure isabove the residual pressure in the coating chamber. In a preferredembodiment of the invention the molten bath is molten copper which isheated by heat from a hollow tube running through the bath. This tube ispreferably heated, in turn, by a gas flame inside thereof.

Referring now to FIGS. 1 and 2 there is illustrated one specificpreferred embodiment of the invention wherein the vacuum chamber isdefined by a wall 10, the vacuum chamber including a coating chamber .12and a sealing chamber 14 through which a substrate 16 is arranged topass. The substrate 16 passes in contact with a drum above a bath 18 ofmolten, aluminum confined in asupport 20 which is illustrated as acarbonaceous crucible. The carbonaceous crucible 2b is preferablysupported by a second container 22 having an outer steel jacket 24 andan inner graphite liner 26. The container 22 confines a mass of moltencopper 28. The heat source, generally indicated at 30, preferablycomprises an outer tube of graphite 32 and an inner tube of a refractorymetal such as alloy steel 34, this inner tube is preferably arranged tobe heated by a gas flame (not shown). In this specific preferredembodiment of the invention, the carbona'ceous crucible '20 ispreferably supported by "a lip 40 which engages a matching lip *42 :onthe popper-holding container 22. A cooled plate 44 is preferablyprovided for clamping the crucible in position to prevent its beinglifted up by the pressure of the moltencopper. This cool plate alsoprevents heat radiation upwardly from the container for the moltencopper. This is particularly useful when the substrate to be coated issensitive to heat.

As best seen in FIG. 2, the inner alloy steel tube (34 of the heatsource extends through the vacuum-tight wall 10 so that it can be atatmospheric pressure. The ends of the alloy steel tube 34 are preferablycooled by suitable cooling coils illustrated at 5010 simplify theforming of a vacuum-tight joint between the tube 34 and the wall 10.

Means are preferably provided to adjust the level of the molten copperand to thereby control the area of contact between the molten copper andthe aluminum-holding crucible. In the preferred :form illustrated, thismeans comprises a graphite piston 52 'whichis -:c'a'rried on Ia .rod 54to permit raising and lowering of the .piston "the molten copper bath.When the piston 52 .is pushed down into the bath it raises the level ofthe bath. Conversely, when the piston is raised the bath level falls.Tllii'sprovides an excellent means for controlling the rate :ofevaporation of the aluminum since .this evaporation rate is a directfunction of the rate of input of .heat to the aluminum, which rate is,in turn, ailirect function of the area of contact between the copper andthe crucible.

In the use of the specific apparatus shown, chambers 12 and 14 areevacuated by suitable-vacuum pumps .(not shown) so as to provide a lowfree air pressure on the order of 1 micron Hg abs. in thecoating-chamber :12. The molten copper is then heated, preferably bymeans of a luminous gas flame inside of tube 34, to a temperature on the.order'of 1400" C. to 1500 C. This 'heatstl're aluminum '18 to atemperature on the order-of 1350" C., at which temperature copiousquantities of aluminum vapors are generated for deposition on asubstrate 16 which is moved over the source of aluminum vapors. When itis desired to slow down the generation of aluminum vapors (for exampledue to the slowing down of the substrate for splicing or otherwise), thegraphite piston 52 is raised, thus lowering the level of the moltencopper and cutting down the rate of heat transfer .to the moltenaluminum. When the 'substrate speed is to be resumed the graphite pistonis again pushed down into the bath of molten copper, thus increasing thegeneration of aluminum vapors.

During the operation of the source, it is preferred that the coolingplate 44 at the top of the source remainsufliciently cool so as to bebelow the melting point of aluminum. Thus any molten aluminum tending tocreep out of the source and over the lip will be'frozen in placeadjacent the lip.

In a preferred embodiment of the invention, a-suitable means is providedfor feeding molten aluminum 'to the source, but for simplicity ofillustration this feeding means has not been shown-in the drawings.

The invention is of utility in connection with the coating of numeroussubstrates such as metals, pawn-plastics, textiles and the like.Equally, it can be applied forproducing metal powders where aluminum isvaporized into an evacuated chamber and is condensed .infree space asdescribed in the copending application of Cerychet al., Serial No.787,055, filed January 15, 1959. Similarly,

the invention can be employed in the production of finely divided metalcompounds by vaporizing metals such as aluminum into a partiallyevacuated space containing a partial pressure of a reactive gas.Similarly, metal vapors can be used to apply thick coatings on suchdiscrete objects as nuts and bolts wherein the objects are to be givencorrosion resisting coats on the order of 1 mil thick. Th metal vaporscan be also used to coat metal powders. For example, magnesium hydridemay be coated with aluminum by passing magnesium hydride in powder formthrough a stream of vapors generated in a source of the type describedabove.

The invention may be utilized for the vaporizing of material other thanaluminum or for vaporizing various organic and inorganic compounds.While copper is a preferred heat transfer medium with the preferredaluminum evaporation, other materials and compounds can be employed inless preferred embodiments of the invention. The principal requirementis that the vapor pressure of the heat transfer medium be lower than thevapor pressure of the material being vaporized at the vaporizationtemperature.

Other physical arrangements of the invention can be employed. Thegraphite crucible 20 can be a long boat, for example, rather than theplurality of individual crucibles illustrated. The crucible 20 may bbuilt up as a compound structure and may be formed of numerous materialswhich are inert either to molten copper or molten aluminum or capable ofsupporting coatings which are inert to these materials. Similarly, thecontainer 22, for holding the molten copper, can assume many differentshapes. It can be subdivided into a number of sections and can havenumerous means for controllably adjusting the level of the molten coppertherein. While one preferred embodiment employing the graphite piston 52has been illustrated, numerous other systems, such as gas pressure andthe like, can be employed if desired. A separate chamber in conjunctionwith chamber 22 can be provided into which the molten copper can bedrained during replacement of the crucibles thus avoiding the necessityof freezing and reheating the copper. The copper can, if desired, befrozen adjacent the outer walls of the container 22 to form a solidskull of the copper. This embodiment of the invention is particularlyfeasible when the aluminum, for example, can be vaporized attemperatures not too greatly in excess of the melting point (1083 C.) ofthe copper. This relatively lower vaporizing temperature for thealuminum is particularly feasible when materials such as strip steel areto be coated. Other sources of heat can be employed in place of theluminous gas flame mentioned previously. This can be a high temperaturesource of heat such as a carbon rod or a refractory metal rod or stripheated to an elevated temperature on the order of 2000 C. Equally,continuous heat can be employed from a graphite or metal heating elementand the heating element can be heated by direct resistance or by inducedcurrents.

The seal chamber 14 mentioned briefly in the foregoing description hasnot been shown in detail in the drawing for simplicity of illustration.It can take many forms, however, such as the slot type seal described inStoll Patent 2,3 84,500. Equally. the substrate 16 can be placed in thechamber 14 in the form of a roll and unwound and rewound in chamber 14without passing through any seal to atmosphere.

Sinc many variations on this basic apparatus can be accomplished withinthe spirit of the invention, it is intended that the description anddrawings herein be taken in a descriptive and non-limiting sense.

What is claimed is:

1. Apparatus for evaporating a material under a high vacuum into avaporization chamber, means for evacuating said vaporization chamber, asupport for holding the material to be evaporated in the vaporizationchamber, a molten bath in contact with the support, a heater formaintaining the molten bath at a temperature sufficiently elevated thatthe material to be evaporated is heated to a temperature Where its vaporpressure is above the residual pressure in the vaporization chamber.

2. Apparatus for coating a substrate by evaporating a material underhigh vacuum in a coating chamber and depositing the material on thesubstrat in the coating chamber, a support for holding the material tobe evaporated in th coating chamber, a molten bath in contact with thesupport, a heater for maintaining the moiten bath at a temperaturesutficiently elevated that the material to be evaporated is heated to atemperature where its vapor pressure is above the residual pressure inthe coating chamber.

3. The apparatus of claim 2 wherein the heater comprises tube meansextending through the molten bath, and means for generating heat insideof said tube means.

4. The apparatus of claim 2 wherein the heater comprises means forgenerating a gas fiow within a tube means passing through the moltenbath.

5. The apparatus of claim 2 wherein the heater comprises an electricalresistant element within a tube means passing through the molten bath.

6. Apparatus for coating a substrate by evaporating aluminum under highvacuum in a coating chamber and depositing the aluminum on the substratein the coating chamber, means for holding a molten bath of copper, aheater for maintaining the molten bath at a temperature sufficientlyelevated that the aluminum to be evaporated is heated to a temperaturewhere its vapor pressure is above th residual pressure in the coatingchamber, a sealed top for said bath-holding means, crucible means forsupporting molten aluminum carried by, and forming a part of, the sealedtop, cooling means adjacent the upper edges of the crucible means.

7. Apparatus for coating a substrate by evaporating aluminum under highvacuum in a coating chamber and depositing the aluminum on the susbtratein the coating chamber, means for holding a molten bath of copper, aheater for maintaining the molten bath at a temperature sufl'icientlyelevated that the aluminum to be evaporated is heated to a temperaurewhere its vapor pressure is above the residual pressure in the coatingchamber, a sealed top for said bath-holding means, crucible means forsupporting molten aluminum carried by, and forming a part of, the sealedtop, cooling means adjacent the upper edges of the crucible means, theupper surface of the crucible means being substantially inert to moltenaluminum and the lower surface of the crucible means being substantiallyinert to the molten bath.

8. Apparatus for coating a substrate by evaporating a material underhigh vacuum in a coating chamber and depositing the material on thesubstrate in the coating chamber, a support for holding the material tobe evaporated in the coating chamber, a molten bath in contact with thesupport, a heater for maintaining the molten bath at a temperaturesufficiently elevated that the material to be evaporated is heated to atemperature where its vapor pressure is above the residual pressure inthe coating chamber, means for raising and lowering the level of themolten bath to change the amount of heat transferred from the moltenbath to the support.

References Cited in the file of this patent UNITED STATES PATENTS1,824,865 Bowden Sept. 29, 1931 2,664,853 Schuler Ian. 5, 1954 2,683,294Bauer et a1. July 13, 1954 2,772,318 Holland Nov. 27, 1956

1. APPARATUS FOR EVAPORATING A MATERIAL UNDER A HIGH VACUUM INTO AVAPORIZATION CHAMBER, MEANS FOR EVACUATING SAID VAPORIZATION CHAMBER,MEANS FOR EVACUATMATEIAL TO BE EVAPORATED IN THE VAPORIZATION CHAMBER, AMOLTEN BATH IN CONTACT WITH THE SUPORT, A HEATER FOR MAINTAINING THEMOLTEN BATH AT A TEMPERATURE SUFFICIENTLY ELEVATED THAT THE MATERIAL TOBE EVAPORATED IS HEATED TO A TEMPERATURE WHERE ITS VAPOR PRESSURE ISABOVE THE RESIDUAL PRESSURE IN THE VAPORIZATION CHAMBER.